In Sydney, more than 1.5 million people watched the shimmering pyrotechnic display designed around the theme "Time to Dream" - a nod to the eagerness many felt in moving forward after the rough year. Big crowds gathered under twinkling holiday lights on Paris' wide Champs Elysees boulevard to pop Champagne corks at midnight and New York's Times Square was awash in optimistic sentiments as it prepared to welcome hordes of New Year 's Eve partiers.
The mood was a bit less bright in Europe, where leaders set the tone for a continent hammered by an unprecedented economic crisis that has put the euro's existence in question, turning in New Year's messages that 2012 will bring more financial hardship - but also opportunities.
Hannah Magauer, a 26-year-old German who was visiting London for New Year's, tried to put a hopeful spin on Chancellor Angela Merkel's warning that 2012 would be more difficult than 2011.
"When you see all of Europe, everything seems to be falling apart and it's a bit scary," she said. "But, at the moment we are very positive we will survive it."
World leaders evoked 2011's events in their New Year's messages. U.N. Secretary-General Ban Ki-moon, who starts his second term on New Year's Day, said he wants to help ensure and sustain the moves toward democracy that protesters sought in the Arab Spring.
Merkel said dealing with Europe's debt crisis would bring its countries closer. Russian Prime Minister Vladimir Putin wished well being and prosperity to all Russians "regardless of their political persuasion" after large-scale protests against him. French President Nicolas Sarkozy, who polls suggest will be defeated by his Socialist challenger in spring elections, warned Europe's crisis is not finished and "that 2012 will be the year full of risks, but also of possibilities."
That ambivalence echoed at the Vatican, where a gold-robed Pope Benedict XVI marked the end of 2011 with prayers of thanks and said humanity awaits the new year with apprehension but also with hope for a better future.
In New York, the crowd cheered as workers lit the crystal-paneled ball that drops at midnight Saturday and put it through a test run, 400 feet (122 meters) above the street. The sphere, now decorated with 3,000 Waterford crystal triangles, has been dropping to mark the new year since 1907, long before television made it a U.S. tradition.
"2012 is going to be a better year. It has to be," said Fred Franke, 53, who was visiting the city with his family even after losing his job in military logistics this month at a Honeywell International division in Jacksonville, Florida.
Authorities in Berlin expected a million revelers to gather around the city's landmark Brandenburg Gate for a massive party complete with live performances from the Scorpions and other bands, as well as a 10-minute long firework display.
In Greece, where the government has imposed especially harsh austerity measures, Prime Minister Lucas Papademos could promise no reprieve.
"A very difficult year is coming: we must continue our effort decisively. So that our sacrifices will not have been in vain," he said.
In light of the warning, Nicholas Adamopoulos, who works as a manager at a pharmaceuticals company, couldn't muster a sunny outlook for the new year.
"You want optimistic people, you go to Brazil," he said.
Thousands of people marched through Edinburgh, some carrying torches or wearing period costumes, on Friday night in preparation for the world-famous Hogmanay street party, where around 80,000 partygoers are welcoming 2012 at the stroke of midnight, before erupting into a mass rendition of Auld Lang Syne.
In London, some 250,000 people are expected to gather to listen to Big Ben strike twelve at midnight during London's scaled-back New Year's celebrations. Fireworks are set off from the London Eye, the giant wheel on the south bank of the river.
Revelers in Spain will greet 2012 by eating 12 grapes in time with Madrid's central Puerta del Sol clock, a national tradition observed by millions who stop parties to follow the chimes on television.
Tens of thousands of young people in the Spanish capital were expected to gather at six indoor "macro-parties" the city council had authorized in big venues such as the city's main sports hall.
Milena Quiroga was to be among the many there happy to move on. "I am glad to see 2011 go because it was a tough year; my restaurant laid off almost half of the staff," said the 25-year-old waitress.
The mood was festive in the South Pacific island nation of Samoa, where, for once, revelers were the first in the world to welcome the new year, rather than the last.
Samoa and neighboring Tokelau hopped across the international date line at midnight on Thursday, skipping Friday and moving instantly to Saturday. The time-jump revelry that began at 12:01 a.m. on Dec. 31 spilled into the night.
Samoa and Tokelau lie near the date line that zigzags vertically through the Pacific Ocean, and both sets of islands decided to realign themselves this year from the Americas side of the line to the Asia side, to be more in tune with key trading partners.
For Japan, 2011 was the year the nation was struck by a giant tsunami and earthquake that left an entire coastline destroyed, nearly 20,000 people dead or missing and the Fukushima Dai-ichi nuclear power plant in meltdown.
"For me, the biggest thing that defined this year was the disaster in March," said Miku Sano, 28, a nursing student in Fukushima city. "Honestly, I didn't know what to say to these people, who had to fight sickness while living in fear about ever being able to go back home. The radiation levels in the city of Fukushima, where I live, are definitely not low, and we don't know how that is going to affect our health in the future."
Raymond Lo, a master of feng shui - the Chinese art of arranging objects and choosing dates to improve luck - offered hope that things might get better. He said he wasn't surprised that 2011 was such a tumultuous year because it was associated with the natural elements of metal and wood. The year's natural disasters were foreshadowed, Lo said, because wood - which represents trees and nature - was attacked by metal.
2012 could be better because it's associated with ocean water, which represents energy and drive and the washing away of old habits, Lo said.
"Big water also means charity, generosity," Lo said. "Therefore that means sharing. That means maybe the big tycoons will share some of their wealth."